Method of preparing a test sample of material for grinding or polishing

ABSTRACT

A grinding and polishing specimen for micro-observation and testing purposes is made by moulding a sample of the material to be tested into a cylindrical or slightly conical block of synthetic resin with a circumferential collar adjacent one end face where the sample is exposed. In placing the specimen in the cavity of a specimen holder, the collar is engaged with the front end of the specimen holder to position the surface of the specimen to be ground or polished accurately with respect to the specimen holder.

United States Pat Diihring et al.

[ METHOD OF PREPARING A TEST SAMPLE OF MATERIAL FOR GRINDING OR POLISHING [75] Inventors: Ornolf Diihring, Bronshoi; Lavritz Gudmund Damgaard, Virum, both of Denmark [73] Assignee: I-I. Struers Chemiske Laboratoriurn,

Copenhagen, Denmark [22] Filed: Feb. 22, 1971 [21] Appl. No.: 117,449

[30] Foreign Application Priority Data Feb. 23, 1970 Denmark 872/70 [52] US. Cl 51/323, 29/527, 51/216 R, 51/277, 264/271, 269/7, 350/92, 425/117 [51] Int. Cl. B23c 3/00 [58] Field of Search 51/323, 216 R, 216 LP,

8/1961 McCormick 29/559 X Oct. 9, 1973 11/1971 Sitte 51/216 RX 3,210,894 10/1965 Bentley 51/277 X 3,120,087 2/1964 Holloway 51/277 X 3,449,870 6/1969 Jensen 51/216 R 2,441,590 5/1948 Ohl 51/277 X 3,081,586 3/1963 Gersbach.... 51/277 X 2,424,835 7/1947 Luckey 51/323 2,668,397 2/1954 Holzrichter 51/323 X 3,514,908 6/1970 Herbert 51/323 X FOREIGN PATENTS OR APPLICATIONS 118,356 4/1944 Australia 51/277 Primary Examiner-Donald G. Kelly Attorney-Watson, Cole, Grindle & Watson [57] ABSTRACT A grinding and polishing specimen for microobservation and testing purposes is made by moulding a sample of the material to be tested into a cylindrical or slightly conical block of synthetic resin with a circumferential collar adjacent one end face where the sample is exposed. In placing the specimen in the cavity of a specimen holder, the collar is engaged with the front end of the specimen holder to position the surface of the specimen to be ground or polished accu rately with respect to the specimen holder.

6 Claims, 8 Drawing Figures PATENTED INVEN TOR A 5km! ATTORNEY METHOD OF PREPARING A TEST SAMPLE OF MATERIAL FOR GRINDING R POLISHING BACKGROUND OF THE INVENTION This invention relates to the grinding or polishing of test samples of material, escpecially samples for microobservation, examination and testing purposes.

In the examination of samples of minerals or other materials, particularly metal alloys, but also ceramic materials and others such as cement, the usual procedure is first to take out a sample of suitable size, as a rule from a few millimeters to a few centimeters, and frequently of irregularshape, whereafter a plane surface is produced on the sample by grinding and polishing. The said surface should be as accurately plane as possible and it should, to the extent possible, be devoid of scratches and show as little disturbance as possible of the original structure of the material. If the material contains grains, which are physically considerably different from the base material, e.g. slag inclusions or graphite, it is a requirement that these do not drop out, but are polished flush with the surface of the sample so that they can be accurately evaluated in a microscopic inspection. The most frequent form of examination is the microscopic inspection, but also micro hardness test and other tests are performed on surfaces prepared in the manner described.

In order to obtain surfaces fulfilling these requirements it is usually necessary to employ several successive grinding and polishing operations. A standard procedure is that upon a rough grinding or cutting by means of a cutting disc a pre-grinding is performed on silicon carbide ,paper under water in up to four stages with decreasing grain size, whereafter the sample is polished by means of diamond paste on polishing discs covered by a polishing cloth, or with aluminum oxide or magnesium oxide on polishing discs covered with felt or wool cloth. The last polishing step may be replaced by electrolytic polishing or mixed electrolyticmechanical polishing, but a pre-grinding on silicon carbide paper is almost always necessary.

Since the samples are frequently of irregular shape and difficult to handle and since a rational and convenient handling is facilitated by using pieces of standardized shape and size, it is usual to embed the samples in a block of synthetic resin before the pre-grinding. This is done either by the so-called heat moulding process or the so-called cold moulding process.The former has the advantage that the specimens produced by this method have a relatively regular and accurate shape, but on the other hand this method is rather expensive and in many cases it is therefore found necessary for practical purposes to use the cold moulding process. In this process there occurs a considerable shrinking of the moulded mass and the specimens will therefore have a rather irregular and inaccurate shape. The shape of grinding and polishing specimens used to-day is always that of a cylindrical block, in which one surface of the sample is located substantially in one end surface of the block. 7

In the preparation of specimens on a large scale machines are used in which a plurality of specimens are treated simultaneously. Such a machine usually has a disc-shaped specimen holder with a number of cavities for receiving the specimens. The specimens are clamped in the cavities by means of screws, and it will be realized that since the clamping takes place on the LII circumferential surface of each specimen the end faces of the specimens will generally not be accurately parallel to the front face of the specimen holder. In order that all specimens may be uniformly ground, every specimen must be ground as much as the most slanting specimen, which results in superfluous grinding work.

Since the surfaces of all the specimens must be located in the same plane during all the grinding and polishing operations, the specimens must remain clamped in the specimen holder until they have been finished. It is impossible to clamp them again in a specimen holder of the same kind and to continue the process without going back to one of the rough grinding stages. If a specimen gets loose, it must be treated all over again from the beginning.

A further drawback of the conventional clamping of the specimens is that gaps are inevitably formed between the cylindrical surface of the specimen and the wall of the cavity of the specimen holder. These gaps may be soiled by grinding dust and must therefore be carefully cleaned to avoid scratches in the subsequent operations. Specimen holders of this type are frequently used for both grinding and polishing, the specimens remaining clamped in the same specimen holder during all the operations.

For the final polishing stage other machines are also in use, in which the samples after having been preground are individually mounted in cylindrical specimen holders serving as weights to produce the necessary pressure against the polishing cloth, the specimen holders being caused to move on a polishing disc or in other manner. One example of such machines is the socalled vibration polishing machine, in which the specimens in their holders are placed on a vibrating plate covered with a polishing cloth and polishing material. Another example is the polishing device described in French patent specification No. 1,572,652 where the specimens in their holders are freely supported on a rotating disc and moved in a path determined by tracks in a guiding disc mounted above the rotating disc.

The mounting of specimens in cylindrical specimen holders is also a delicate problem which has not so far been solved in a perfectly satisfactory manner. In this case, too, it is difficult to obtain parallelism between the front face of the specimen and that of the holder, and since the holders are frequently rather tall in order to obtain a sufficient polishing pressure, the specimens in their holders will tend to become tilted if the front face of the specimen is not perpendicular to the axis of the holder.

SUMMARY OF THE INVENTION It is the object of the invention to reduce or eliminate the drawbacks described. According to the invention a method is provided of bringing a sample of material in readiness for grinding or polishing for microobservation, examination and testing purposes. Like in the known methods a grinding or polishing specimen is first made by moulding the sample into a substantially cylindrical block in such a manner that one surface of the sample is located substantially in one end surface of the block, referred to in the following as its front end, and said specimen is subsequently mounted in substantially cylindrical cavity of a specimen holder in a position such that its front end extends beyond a front face of the holder. According to the invention, said block is moulded in such a manner as to form a portion projecting from the circumferential surface of the block adjacent its front end and forming a rearwardly facing shoulder along the circumference of the block, and said specimen is subsequently introduced into the cavity of said holder from the front end thereof, said shoulder of said specimen being pressed into engagement with the front face of said holder.

The advantages of using this procedure may briefly be summarized as follows:

1. When a plurality of specimens are mounted in a specimen holder, all the specimens will extend the same distance from the front face of the specimen holder and will be parallel to each other with a very good approximation.

2. The force pressing the sample against the grinding paper is taken up by the shoulder of the specimen so that there will be no tendency towards displacement of the specimen in the axial direction. A very small clamping force will therefore suffice to prevent the specimens from rotating about their own axis, where this is found necessary.

3. Even if the specimen should rotate about its own axis, only very small deviations from parallelism will occur.

4. The very weak clamping may be obtained by resilient forces, e.g. by means of an O-ring mounted in the cavity of the specimen holder.

5. The gap between the specimen and the wall of the cavity is closed by the shoulder portion which is usually in the form ofa collar so that grinding dust cannot penetrate into the cavity.

6. There is no risk that a specimen become displaced during the process and therefore will not become adequately ground or polished.

7. Since the collar secures parallelism, the specimens, when subsequently mounted in an individual specimen holder, will automatically have their front face perpendicular to the axis of the holder and extend a suitable distance beyond the front end of the holder. They may be held in the cavity either by means of an O-ring or by springs.

8. Since no care is required for adjusting and clamping the specimens in the holder, a considerable saving of time is obtained in the mounting operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows one form of a polishing and grinding specimen according to the invention, in vertical sectron,

FIG. 2 a section through a specimen holder, in which the specimen of FIG. 1 is mounted,

FIG. 3 a specimen according to another embodiment of the invention,

FIG. 4 a horizontal section through the portion of a specimen holder according to an embodiment of the invention immediately surrounding a cavity thereof,

FIG. 5 a corresponding vertical section,

FIG. 6 a specimen for mounting in the specimen holder of FIGS. 4 and 5,

FIG. 7 a cavity of a specimen holder for receiving the specimen of FIG. 8, and

FIG. 8 a specimen according to a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a specimen, in which a sample 1 is moulded into a cylindrical block 2 of synthetic resin, said block being provided with a collar 3 forming a rearwardly facing shoulder 4. In FIG. 2 the specimen of FIG. 1 is shown as mounted in a cavity 5 of a specimen holder 6, the shoulder 4 engaging the front face of the specimen holder 6, whereby the front face of the specimen will be parallel to the front face of the specimen holder and located at a predetermined distance in front of same with very good approximation. If the front face of the specimen is not from the start absolutely parallel to the front face of the specimen holder, it will become so parallel in the first grinding step and remain so even if the specimen is taken out and e.g. mounted in another specimen holder. For this purpose it is not necessary that the shoulder 4 is absolutely plane, as long as the front face of the specimen holder is plane. Instead of a continuous collar it would be possible to use at least three discrete projections distributed along the circumference of the specimen.

The specimen should be sufficiently movable in the cavity to permit engagement of the shoulder 4 with the front face of the specimen holder. It may e.g. have a slightly smaller diameter than the cavity and be held therein by means of an O-ring 7, as illustrated in FIG. 2. The specimen may also be slightly conical.

In the embodiment illustrated in FIG. 3, the block 2 is moulded in a remaining shell 8, on which the collar 3 is formed. Thus, the shell 8 is used both as a mould in the preparation of the specimen and as a remaining part of the specimen. In the moulding operation the shell 8 is placed in a recess ofa supporting plate. A circumferential rib 9 on the inner wall of the shell 8 prevents the shell from creeping under the influence of axial grinding forces. It has been found that when producing the shell 8 from suitable synthetic resin, such as polyethylene, the shell will follow the shrinkage of the mould material of the block 2 sufficiently to prevent cracking.

FIG. 4 shows a specimen holder 10, in which the wall of the cavity 11 is constructed with teeth 12, which are capable of cutting into the circumferential surface of the specimen thereby deforming the corresponding portions of the specimen so that the shoulder 4 may be pressed into engagement with the front face of the specimen holder. The teeth should be so constructed that they do not cut chips because loose particles might form an obstacle to the accurate engagement of the collar against the front face of the specimen holder. By the deformation of the surface of the specimen taking place by the penetration of the teeth into the surface the specimen is firmly held. It is important that the collar of the specimen should be pressed fully into engagement with the front face of the specimen holder. To secure this a small hand press may if required be used for pushing the specimen into the cavity of the holder.

FIG. 8 shows a specimen on the circumferential surface of which deformable ribs 13 tapering in the upward direction are provided. In the specimen holder for receiving such a specimen 14, see FIG. 7, the cavity should be constructed with a slightly rounded edge 15 in order to cut chips. When the specimen is pressed into the specimen holder, the ribs are deformed so that it becomes possible to engage the collar 3 fully with the front face of the specimen holder, if required by means of a hand press. In the embodiment illustrated in FIG. 8, the ribs 3 are formed on a shell of the kind illustrated in FIG. 3, but such ribs may of course also be formed on any other form of specimen within the scope of the invention.

We claim:

1. A method of preparing a sample of material for grinding or polishing for micro-observation, examina' tion and testing purposes, said method comprising the steps of:

forming a grinding or polishing specimen by moulding a sample into an elongated block in such a manner that one surface of the sample is located substantially in one end surface of the block, said one end being referred to in the following as the front end of the block;

providing a specimen holder having a substantially cylindrical cavity configured to receive said elongated grinding or polishing specimen, said holder having a front face surrounding said cavity,

said block being configured to fit loosely into said cavity and having a portion projecting radially outwardly therefrom adjacent said front end to present a rearwardly facing shoulder disposed along the circumference of the block; and

inserting said specimen into said cavity of said holder in a manner to press said shoulder of said specimen into engagement with the front face of said holder without rigidly securing said specimen in said cavity.

2. A method as set forth in claim 1, comprising the further step of providing means for yieldably holding the specimen in the cavity after said inserting step.

3. A method as set forth in claim 2 wherein said means comprises a sealing ring disposed between said block and the internal wall of the cavity.

4. A method as set forth in claim 3 wherein said means comprises longitudinally extending ribs projecting from the circumferential surface of the block behind the shoulder, said ribs tapering in a direction away from said shoulder, said insertion step including deforming the ribs by engagement thereof with the walls of the cavity whereby to permit said engagement of the shoulder with the front of the specimen holder.

5. A method as set forth in claim 3 wherein said means comprises portions projecting from the internal wall of the cavity adapted for cutting into the circumferential surface of a specimen inserted into the cavity, said insertion step including deforming the circumferential surface of a specimen inserted into the cavity by engagement thereof with said portions whereby to permit said engagement of the shoulder with the front face of the specimen holder.

6. A method as set forth in claim 1 wherein said specimen is formed by moulding a first section of the block which contains the sample into a preformed second section of the block which includes the projecting portion. 

1. A method of preparing a sample of material for grinding or polishing for micro-observation, examination and testing purposes, said method comprising the steps of: forming a grinding or polishing specimen by moulding a sample into an elongated block in such a manner that one surface of the sample is located substantially in one end surface of the block, said one end being referred to in the following as the front end of the block; providing a specimen holder having a substantially cylindrical cavity configured to receive said elongated grinding or polishing specimen, said holder having a front face surrounding said cavity, said block being configured to fit loosely into said cavity and having a portion projecting radially outwardly therefrom adjacent said front end to present a rearwardly facing shoulder disposed along the circumference of the block; and inserting said specimen into said cavity of said holder in A manner to press said shoulder of said specimen into engagement with the front face of said holder without rigidly securing said specimen in said cavity.
 2. A method as set forth in claim 1, comprising the further step of providing means for yieldably holding the specimen in the cavity after said inserting step.
 3. A method as set forth in claim 2 wherein said means comprises a sealing ring disposed between said block and the internal wall of the cavity.
 4. A method as set forth in claim 3 wherein said means comprises longitudinally extending ribs projecting from the circumferential surface of the block behind the shoulder, said ribs tapering in a direction away from said shoulder, said insertion step including deforming the ribs by engagement thereof with the walls of the cavity whereby to permit said engagement of the shoulder with the front face of the specimen holder.
 5. A method as set forth in claim 3 wherein said means comprises portions projecting from the internal wall of the cavity adapted for cutting into the circumferential surface of a specimen inserted into the cavity, said insertion step including deforming the circumferential surface of a specimen inserted into the cavity by engagement thereof with said portions whereby to permit said engagement of the shoulder with the front face of the specimen holder.
 6. A method as set forth in claim 1 wherein said specimen is formed by moulding a first section of the block which contains the sample into a preformed second section of the block which includes the projecting portion. 